The invention pertains to a coating composition comprising a first compound comprising at least one bicyclo- or spiro-orthoester group.
The use of compounds comprising bicyclo-orthoester groups in coating compositions is known from U.S. Patent publication No. 4,338,240. In this patent publication the use and the preparation of bicyclo-orthoester-functional compounds (hereinafter bicyclo-orthoester will be abbreviated to BOE) is described. Described are, e.g., BOE-functional compounds, which are the adduct of two compounds comprising one hydroxyl group and one BOE group and one compound comprising two isocyanate groups. The compounds are cross-linked by means of cationic ring opening homopolymerization of the BOE groups. In that case, however, the presence of moisture has to be excluded. Furthermore, energy in the form of ultraviolet, infrared or microwave irradiation or heat has to be supplied during the polymerization process.
The invention now provides a coating composition of the aforementioned type which is free of said drawbacks. For that reason the coating composition mentioned in the opening paragraph is characterized in that it comprises a second compound comprising at least two hydroxyl-reactive groups.
A coating composition comprising a compound comprising at least one bicyclo- or spiro-orthoester group (hereinafter spiro-orthoester will be abbreviated to SOE) is a composition having latent hydroxyl groups. In the presence of water or moisture from the air the BOE or SOE groups will be hydrolyzed, forming hydroxyl groups. This reaction is also known as deblocking. During deblocking few if any volatile components are released. When the BOE- or SOE-group is deblocked in this manner, it is not possible to obtain a homopolymer of BOE- or SOE groups by cationic polymerization. However, it has now been found that when a second compound comprising at least two hydroxyl-reactive groups is present in the composition, the deblocked hydroxyl groups can react with the hydroxyl-reactive groups to give a cross-linked polymer.
BOE- and SOE-functional compounds may be used as main binders or as reactive diluents in the coating compositions of the present invention.
The use of compounds comprising BOE or SOE groups in coating compositions has several advantages over the use of compounds having free hydroxyl groups, such as hydroxyl-functional reactive diluents, hydroxyl-functional main binders, e.g. polyester polyols and acrylate polyols, and even compounds where the BOE or SOE groups have already been hydrolyzed.
Firstly, the viscosity of compounds comprising BOE or SOE groups is lower than that of the corresponding hydrolyzed compounds. In consequence, less viscosity-reducing solvent which evaporates in air is needed in the coating composition.
Secondly, because of the stability of the BOE- and SOE-functional compounds the pot life:drying time ratio of compositions according to the invention is particularly favorable, for hydrolysis only takes place in the presence of water or moisture.
Thirdly, in coating compositions of the present invention BOE- and SOE functional compounds have the advantage that hydrolysis of the BOE or SOE group produces a substantial increase in the composition""s viscosity. A high viscosity will give reduced sagging of the coating composition on the substrate.
Finally, it has been found that the coating compositions of the present invention provide a high build behavior.
By BOE groups are meant in this connection groups having a structure according to formula I 
wherein
X and Z are independently from each other selected from linear or branched alk(en)ylene groups with 1-4 carbon atoms optionally containing an oxygen or a nitrogen atom;
Y is nothing or is selected independently of X and Z from linear or branched alk(en)ylene groups with 1-4 carbon atoms optionally containing an oxygen or a nitrogen atom;
R1 and R2 may be the same or different and are selected from the group of monovalent radicals comprising
hydrogen, hydroxyl, alk(en)yl groups comprising 1-30 carbon atoms which may be linear or branched and may optionally contain one or more heteroatoms and groups selected from the group of oxygen, nitrogen, sulphur, phosphorus, sulphone, sulphoxy, and ester, optionally substituted with epoxy, cyano, amino, thiol, hydroxyl, halogen, nitro, phosphorus, sulphoxy, amido, ether, ester, urea, urethane, thioester, thioamide, amide, carboxyl, carbonyl, aryl, and acyl groups, and
divalent radicals comprising
alk(en)ylene groups having 1-10 carbon atoms which groups may be linear or branched and may optionally contain one or more heteroatoms and groups selected from the group of oxygen, nitrogen, sulphur, phosphorus, sulphone, sulphoxy, and ester, optionally substituted with epoxy, cyano, amino, thiol, hydroxyl, halogen, nitro, phosphorus, sulphoxy, amido, ether, ester, urea, urethane, thioester, thioamide, amide, carboxyl, carbonyl, aryl, and acyl groups, ester groups; ether groups; amide groups; thioester groups; thioamide groups; urethane groups; urea groups; and a single bond.
Preferably, X, Y, and Z are methylene. R1 and R2 in that case are linked to a divalent 2,6,7-trioxabicyclo[2.2.2]octane radical.
In the case of R1 and R2 being both monovalent radicals, the BOE group as defined by formula I is the same as the BOE-functional compound. Monovalent radicals R1 and R2 are preferably independently from each other selected from the group of hydrogen, hydroxyl, and linear or branched alk(en)yl groups having 1-20 carbon atoms, optionally substituted with one or more hydroxyl groups and optionally comprising an ester group. Examples of such groups are: methyl, methylol, ethyl, ethylol, propyl, propylol, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, a xe2x80x94CH2xe2x80x94CH2xe2x80x94Oxe2x80x94COxe2x80x94C1-20 alk(en)yl group, and mixtures thereof.
Preferably, R1 is linear or branched alk(en)yl having 1-20 carbon atoms, optionally substituted with hydroxyl, while R2 is methyl or ethyl. Alternatively, R1 can be methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and mixtures thereof, while R2 can be methylol, ethyl, ethylol or a xe2x80x94CH2xe2x80x94CH2xe2x80x94Cxe2x80x94COxe2x80x94C1-20 alk(en)yl group.
When a divalent radical is selected for either or both R1 or R2 groups, high-molecular weight BOE-functional compounds can be formed. These may be adducts or polymers comprising several BOE groups. Thus two BOE groups can form an adduct by selecting a monovalent radical for one of the two R1 and R2 groups, and a divalent radical for the other. The BOE groups will then be linked together via the divalent radical. BOE groups may also be linked via the divalent radicals to monomer or oligomer compounds. Such BOE-functional compounds are, e.g. described in above-mentioned U.S. Pat. No. 4,338,240. For example, two BOE groups may be linked to a dimer fatty acid, e.g. xe2x80x9cPRIPOL(copyright)xe2x80x9d 1009 (available from Unichema Chemie BV, Gouda, Netherlands). Alternatively, in the aforementioned configuration the BOE groups can function as side groups or terminal groups in a polymer chain. The polymers can be, e.g., polyesters, polyethers, polyacrylates, polyamides or polyurethanes. When the divalent radical is a single bond, the BOE group is bonded directly to the polymer. When the R1 and R2 groups are both divalent, the BOE groups can be incorporated into the main chain of a polymer or they can serve to link two polymer chains together. Preferably, one or both R1 and R2 groups are selected from the group of ester, ether, urethane, a single bond, and alk(en)ylene groups having 1-10 carbon atoms which may be linear or branched and may contain one or more ester, ether, or urethane groups.
The term SOE groups in this case refers to groups having a structure according to formula II or III 
wherein
R3 and R5 are independently from each other selected from the group of linear or branched alk(en)yl, aryl or acyl optionally containing one or more oxygen, nitrogen, sulphur or phosphorus atoms, optionally substituted with a halogen atom; and
R4 and R6 are independently from each other selected from an alkylene group having 1-3 carbon atoms optionally substituted with one or more groups selected from monovalent radicals
such as linear or branched alk(en)yl, aryl or acyl groups optionally containing one or more oxygen, nitrogen, sulphur, and phosphorus atoms; and
divalent radicals
such as a single bond and an alkylene group having 1-10 carbon atoms with or without one or more atoms and groups selected from oxygen, nitrogen, sulphur, and phosphorus atoms, and ether, ester, and urethane groups.
Preferably, R3 and R5 are selected independently from linear or branched alk(en)yl groups having 1-4 carbon atoms, e.g., a methyl or ethyl group.
In the case that neither of R4 and R6 is substituted with a divalent radical, the SOE group as defined by formulae II and III is the same as the SOE-functional compound.
When a divalent radical is selected as substituent for either or both R4 and R6 groups, high-molecular weight SOE-functional compounds can be prepared in the same manner as described above for high-molecular BOE compounds. When R4 or R6 has one divalent radical substituent, adducts or polymers can be made which have SOE groups as terminal or side groups. In formula III, R4 and R5 can both have divalent radicals as substituents, in which case the SOE group can be incorporated into the main chain. The polymers may be, e.g., polyacrylate, polyester, polyether, polyamide or polyurethane.
Alternatively, R4 can be 
with the compound formed being point symmetrical to CS, giving a SOE compound according to formula IV: 
Preferably, formula IV is: 
Preferably, R4 is ethylene, optionally substituted with a linear or branched alkyl group having 1-5 carbon atoms, optionally containing one or more oxygen and nitrogen atoms. For instance, R4 may be: 
Preferably, R6 is propylene.
In addition to the BOE- or SOE-functional compound the coating composition according to the invention comprises a second compound comprising at least two hydroxyl-reactive groups. The hydroxyl-reactive groups are selected from the group of isocyanate, epoxy, acetal, carboxyl, anhydride, and alkoxy silane groups. Also, mixtures of these groups in one compound are included. Alternatively, the second compound can be an amino resin.
Examples of compounds comprising at least two isocyanate groups are aliphatic, alicyclic, and aromatic polyisocyanates such as trimethylene diisocyanate, 1,2-propylene diisocyanate, tetramethylene diisocyanate, 2,3-butylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 2,4-trimethyl hexamethylene diisocyanate, 2,4,4-trimethyl hexamethylene diisocyanate, dodecamethylene diisocyanate, xcex1,xcex1xe2x80x2-dipropyl ether diisocyanate, 1,3-cyclopentylene diisocyanate, 1,2-cyclohexylene diisocyanate, 1,4-cyclohexylene diisocyanate, 4-methyl-1,3-cyclohexylene diisocyanate, 4,4xe2x80x2-dicyclohexylene diisocyanate methane, 3,3xe2x80x2-dimethyl-4,4xe2x80x2-dicyclohexylene diisocyanate methane, m- and p-phenylene diisocyanate, 1,3- and 1,4-bis(isocyanate methyl) benzene, 1,5-dimethyl-2,4-bis(isocyanate methyl) benzene, 1,3,5-triisocyanate benzene, 2,4- and 2,6-toluene diisocyanate, 2,4,6-toluene triisocyanate, xcex1,xcex1,xcex1xe2x80x2,xcex1xe2x80x2-tetramethyl o-, m-, and p-xylylene diisocyanate, 4,4xe2x80x2-diphenylene diisocyanate methane, 4,4xe2x80x2-diphenylene diisocyanate, 3,3xe2x80x2-dichloro-4,4xe2x80x2-diphenylene diisocyanate, naphthalene-1,5-diisocyanate, isophorone diisocyanate, and transvinylidene diisocyanate and mixtures of the aforementioned polyisocyanates.
Also, such compounds may be adducts of polyisocyanates, e.g., biurets, isocyanurates, allophonates, uretdiones, and mixtures thereof. Examples of such adducts are the adduct of two molecules of hexamethylene diisocyanate or isophorone diisocyanate and a diol such as ethylene glycol, the adduct of 3 molecules of hexamethylene diisocyanate and 1 molecule of water, the adduct of 1 molecule of trimethylol propane and 3 molecules of isophorone diisocyanate, the adduct of 1 molecule of pentaerythritol and 4 molecules of toluene diisocyanate, the isocyanurate of hexamethylene diisocyanate, available from Bayer Aktiengesellschaft (Federal Republic of Germany) under the trade designation xe2x80x9cDESMODUR(copyright)xe2x80x9d N3390, the uretdione of hexamethylene diisocyanate, available from Bayer under the trade designation xe2x80x9cDESMODUR(copyright)xe2x80x9d N3400, the allophonate of hexamethylene diisocyanate, available from Bayer under the trade designation xe2x80x9cDESMODUR(copyright)xe2x80x9d LS2101, and the isocyanurate of isophorone diisocyanate, available from Hxc3xcls under the trade designation xe2x80x9cVESTANATE(trademark)xe2x80x9d T1890. Furthermore, (co)polymers of isocyanate-functional monomers such as xcex1,xcex1xe2x80x2-dimethyl-m-isopropenyl benzyl isocyanate are suitable for use. Finally, the above-mentioned isocyanates and adducts thereof may be present in the form of blocked isocyanates as known to the skilled man.
Examples of compounds comprising at least two epoxy groups are solid or liquid epoxy compounds, such as the di- or polyglycidyl ethers of aliphatic, cycloaliphatic, or aromatic hydroxyl compounds such as ethylene glycol, glycerol, cyclohexane diol, mononuclear di- or polyvalent phenols, bisphenols such as Bisphenol-A and Bisphenol-F, and polynuclear di- or polyvalent phenols; polyglycidyl ethers of phenol formaldehyde novolac; epoxidized divinyl benzene; epoxy compounds comprising an isocyanurate group; an epoxidized polyalkadiene such as epoxidized polybutadiene; hydantoin epoxy resins; epoxy resins obtained by epoxidizing aliphatic and/or cycloaliphatic alkenes, such as dipentene dioxide, dicyclopentadiene dioxide, and vinylcyclohexene dioxide; and glycidyl groups-comprising resins, such as polyesters or polyurethanes having two or more glycidyl groups per molecule; or mixtures of the aforementioned epoxy compounds. Preferably, use is made of the aforementioned cycloaliphatic compounds comprising two or more epoxy groups.
Alternatively, use is made of a (co)polymer of ethylenically unsaturated epoxy groups comprising compounds such as glycidyl(meth)acrylate, N-glycidyl(meth)acrylamide and/or allyl glycidyl ether and, if so desired, one or more copolymerizable, ethylenically unsaturated monomers.
Examples of compounds comprising at least two acetal groups are disclosed, int. al., in patent publications U.S. Pat. No. 4,788,288, U.S. Pat. No. 4,864,055, U.S. Pat. No. 5,155,170, and U.S. Pat. No. 5,336,807. Other suitable acetal-functional compounds include compounds obtained by reacting aminobutyraldehyde di(m)ethyl acetal (ABDA) and carboxyl ester-, isocyanate- or cyclocarbonate-functional (co)oligomers or (co)polymers, e.g., polyester, polyacrylate, and polyurethane. An example of such a polymer includes the copolymer of glycerol cyclocarbonate methacrylate and styrene. Also, mixtures of compounds comprising at least two acetal groups can be employed.
Examples of compounds comprising at least two carboxyl groups include saturated or unsaturated aliphatic, cycloaliphatic, and aromatic polycarboxylic acids, such as malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, decane dicarboxylic acid, dimer fatty acid, maleic acid, tetrahydrophthalic acid, hexahydrophthalic acid, hexahydroendomethylene tetrahydrophthalic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, 3,6-dichlorophthalic acid, tetrachlorophthalic acid, and mixtures thereof.
Examples of anhydride-functional compounds include radical polymers of an unsaturated cyclic anhydride monomer, e.g., maleic acid anhydride, itaconic acid anhydride, or citraconic acid anhydride. Furthermore, copolymers of said anhydride monomers and one or more ethylenically unsaturated monomers can be employed. These copolymers may contain 10-50 wt. % of anhydride groups. Examples of ethylenically unsaturated monomers are styrene, substituted styrene, vinyl chloride, vinylacetate, and esters of acrylic or methacrylic acid, e.g., methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, butyl(meth)acrylate, t-butyl(meth)acrylate, n-hexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, cyclohexyl(meth)acrylate, 2,2,5-trimethyl cyclohexyl(meth)acrylate, and isobornyl(meth)acrylate. The anhydride-functional (co)polymer may contain small quantities, e.g., 1 to 10 wt. %, of ethylenically unsaturated carboxylic acid groups, e.g., (meth)acrylic acid. The molecular weight of the anhydride-functional (co)polymer preferably is 1,000-50,000.
When the coating composition according to the present invention is used as a top coat, the aforesaid ethylenically unsaturated monomer preferably is used in a molar ratio of 1:1 with the anhydride monomer, as described in U.S. Pat. No. 4,798,745.
Alternatively, the anhydride-functional compound can be an adduct of an anhydride monomer and a functional group-comprising polymer. Examples of such adducts are: the adduct of polybutadiene or a butadiene/styrene copolymer and maleic acid anhydride; the adduct of maleic acid anhydride and a styrene/allyl alcohol copolymer esterified with an unsaturated fatty acid, resins of terpene and maleic acid anhydride; adducts of hydroxyl-comprising polymers and anhydride monomers, e.g., copolymers of hydroxyethyl(meth)acrylate or styrene/allyl alcohol and a tricarboxylic compound capable of forming anhydride groups, such as described in EP-A-0 025 917; the adduct of trimellitic acid anhydride and a polyol, such as described in EP-A-0 134 691; and the adduct of a thiol groups-comprising polymer and an unsaturated cyclic anhydride such as maleic acid anhydride, itaconic acid anhydride or citraconic acid anhydride. Also, mixtures of anhydride-functional compounds can be employed.
Examples of alkoxysilane-functional compounds are alkoxysilanes of the following general formula: 
wherein T is a hydrolyzable group such as xe2x80x94OCH3, xe2x80x94OC2H5 or xe2x80x94OC2H4OCH3 and
R7 and R8 are reactive groups selected independently from each other. Examples of such reactive groups include vinyl, aminoalkyl, epoxyalkyl, and methacryloxyalkyl groups. Also, reaction products of alkoxysilane-functional compounds and mixtures of alkoxysilane-functional compounds and/or reaction products of these can be employed.
Examples of vinyl-functional alkoxysilanes include vinyl triethoxysilane and vinyl trimethoxysilane As an example of a reaction product of a vinyl-functional alkoxysilane may be mentioned the silicone resin formed by the reaction of (CH2xe2x95x90CHSiO{fraction (3/2)})x(R2SiO)y and styrene.
Reaction products of amino-functional alkoxysilanes can be made by reacting such silanes with inorganic acids HA:
NH2(CH2)3Si(T)3+HAxe2x86x92Axe2x86x92NH(CH2)3Si(T)3
wherein A is the acid radical ion, or with esters of organic acids R9(COOR10)n, wherein n is an integer of at least 1, R9 is a linear or branched, optionally unsaturated, alkane radical, and R10 is a lower alkyl group, e.g., a C1-4 alkyl group, e.g.:
NH2(CH2)3Si(T)3+R9COOR10xe2x86x92R9COxe2x80x94NH(CH2)3Si(T)3 
2NH2(CH2)3Si(T)3+1R10OOCR9COOR10xe2x86x92
(T)3Si(CH2)3NHxe2x80x94OCR9COxe2x80x94NH(CH2)3S i(T)3. 
For example, the adduct of 1 mole diethyl malonate and 2 moles of 3-amino propyl trimethoxy silane is a suitable alkoxy silane containing compound. Also suitable for use are reaction products of amino-functional alkoxysilanes and isocyanate-functional compounds.
One example of a reaction product of an epoxy-functional silane compound is the reaction product of xcex2-(3,4-epoxycyclohexyl) ethyl trimethoxysilane and amines, acids, and alcohols.
Examples of reaction products of methacryloxyalkyl trialkoxysilane are reaction products of xcex3-methacryloxypropyl trimethoxysilane and xcex3-methacryloxypropyl tri(xcex2-methoxyethoxy)silane and vinyl-functional monomers, such as styrene and methyl methacrylate.
Examples of suitable amino resins are urea resins, guanamine resins, and melamine resins, and mixtures of these. Examples of urea resins are etherified methylol urea, butyl urea, and isobutyl urea. One example of a guanamine resin is tetra(methoxymethyl)benzoguanamine. Examples of melamine resins are hexa(methoxymethyl)melamine (HMMM) and isobutylated melamine.
In addition to the disclosed BOE- and SOE-functional compounds and said hydroxyl-reactive compounds other compounds may be present in the coating composition according to the present invention. Such compounds may be main binders and/or reactive diluents comprising reactive groups which may be cross-linked with the aforesaid hydroxyl-functional compounds and/or hydroxyl-reactive compounds. Examples include hydroxyl-functional binders, e.g., polyester polyols such as described in H. Wagner et al., Lackkunstharze, 5th ed., 1971 (Carl Hanser Verlag, Munich), polyether polyols, polyacrylate polyols, polyurethane polyols, cellulose acetobutyrate, hydroxyl-functional epoxy resins, alkyds, and dendrimeric polyols such as described in WO 93/17060. Also, hydroxyl-functional oligomers and monomers, such as castor oil and trimethylolpropane may be present. Finally, ketone resins, aspargyl acid esters, and latent or non-latent amino-functional compounds such as oxazolidines, ketimines, aldimines, diimines, secondary amines, and polyamines may be present. These and other compounds are known to the skilled person and are mentioned, int. al., in U.S. Pat. No. 5,214,086.
The ratio of hydroxyl-reactive groups to hydroxyl groups ranges from 50 to 300 eq. %, preferably from 70 to 250 eq. %
The invention further encompasses a process for curing the present coating composition. More particularly, the latent hydroxyl groups of the BOE or SOE-functional compound have to be deblocked and reacted with the hydroxyl-reactive groups of the second compound to allow the present coating composition to be cured.
The deblocking of the latent hydroxyl groups of the BOE and SOE compounds takes place under the influence of water in the form of, e.g., moisture from the air or added water. This deblocking is preferably catalyzed by a first catalyst selected from the group of Lewis acids, such as AlCl3, SbCl5, BF3, BCl3, BeCl2, FeCl3, FeBr3, SnCl4, TiCl4, ZnCl2 and ZrCl4 and organic complexes thereof, e.g., BF3-Et2O, BF3-2CH3COOH, BF3-2H2O, BF3xe2x80x94H3PO4, BF3xe2x80x94(CH3)2O, BF3xe2x80x94THF, BF3-2CH3OH, BF3-2C2H5OH, and BF3xe2x80x94C6H5CH2, and Brxc3x8nsted acids. Preferably, use is made of Brxc3x8nsted acids having a pKa less than 3, such as a mono- or dialkyl phosphate, a carboxylic acid having at least one chlorine and/or fluorine atom, an alkyl or aryl sulphonic acid or an (alkyl)phosphoric acid, more particularly methane sulphonic acid, paratoluene sulphonic acid, optionally substituted naphthalene sulphonic acids, dodecyl benzene sulphonic acid, dibutyl phosphate, trichloroacetic acid, phosphoric acid, and mixtures thereof.
Said first catalysts may be blocked, if so desired, resulting in the release of the Lewis or Brxc3x8nsted acid under the influence of, e.g., electromagnetic irradiation (light or UV), heat or moisture. Acid generating photoinitiators are described, int. al., in G. Li Bassi et al., xe2x80x9cPhotoinitiators for the Simultaneous Generation of Free Radicals and Acid Hardening Catalysts,xe2x80x9d Radcure ""86 Proceedings, e.g. 2-methyl-1-[4-(methylthio)phenyl]-2-[4-methylphenylsulphonyl]propan-1-one (MDTA), ex. Fratelli Lamberti Spa, Varese, Italy. Alternatively, use may be made of Lewis acid generating compounds such as xe2x80x9cIRGACURE(copyright)xe2x80x9d 261 (available from Ciba Geigy, Tarrytown, N.Y.) and trimethyl silyl benzene sulphonic ester.
The first catalyst can be used alone or as a mixture of catalysts in effective amounts. The term effective amount in this case is dependent on the use of the BOE- or SOE-functional compound. When the BOE- or SOE-functional compound is used as a main binder, sufficient catalyst will have to be present to hydrolyze practically all BOE- or SOE-functional compounds. However, if the BOE- or SOE-functional compound is used primarily as a reactive diluent while other compounds are present as main binders, the hydrolyzation of at least a portion of the BOE- or SOE-functional compound will suffice.
Amounts of 0 to 10 wt. % relative to the BOE- and SOE-functional compounds of the first catalyst may be sufficient. Preferably, 0.3 to 8 wt. %, more specifically, 0.5 to 6 wt. %, will be present.
The reaction of the deblocked hydroxyl groups of the BOE or SOE compound, the hydroxyl-reactive groups of the second compound, and, optionally, third compounds present in the composition comprising hydroxyl groups or hydroxyl-reactive groups, takes preferably place under the influence of a second catalyst. Such catalysts are known to the skilled person. The second catalyst is used in an amount of 0 to 10 wt. %, preferably 0.001 to 5 wt. %, more preferably in an amount of 0.01 to 1 wt. %, calculated on solid matter (i.e., the amount of BOE or SOE, the hydroxyl-reactive compound, and, optionally, the above-mentioned third compounds).
As an example for the various hydroxyl-reactive groups the following catalysts may be mentioned. Polyisocyanates: dimethyl tin dilaurate, dibutyl tin dilaurate, dibutyl tin diacetate, tin octoate, zinc octoate, aluminum chelate, and dimethyl tin dichloride; polyepoxy compounds: tertiary amines and Lewis acids such as BF3 or organic complexes thereof; polyacetal compounds: paratoluene sulphonic acid and dodecyl benzene sulphonic acid; polycarboxylic compounds: dodecyl benzene sulphonic acid, polyanhydride compounds: organotin compounds; alkoxysilane compounds: organotin compounds, phosphoric acid, paratoluene sulphonic acid, dodecyl benzene sulphonic acid, and tertiary amines; and amino resins: dodecyl benzene sulphonic acid.
As can be noted from the above, the first and the second catalyst may be the same in some coating compositions. In that case, the amount of catalyst may be higher than indicated for the first or second catalyst alone.
The coating composition according to the invention may be part of a components system, for instance a 2-component system. For example, one component may comprise both the BOE- or SOE-functional compound and the hydroxyl-reactive compound. The second component may comprise the catalyst for the hydrolysis of the BOE- or SOE-functional compound.
Alternatively, a 3-component system may be employed. For example, one component may comprise the BOE- or SOE-functional compound. A second component may comprise the hydroxyl-reactive component. A third component may comprise the catalyst for the hydrolysis of the BOE- or SOE-functional compound.
In addition, a coating composition such as described may contain the usual additives such as solvents, pigments, fillers, leveling agents, emulsifiers, anti-foaming agents and rheology control agents, reducing agents, antioxidants, HALS-stabilisers, UV-stabilizers, water traps such as molecular sieves, and antisettling agents.
Application onto a substrate can be via any method known to the skilled person, e.g., via rolling, spraying, brushing, flow coating, dipping, and roller coating. Preferably, a coating composition such as described is applied by spraying.
The coating composition of the present invention may be applied to any substrate. The substrate may be, for example, metal, e.g., iron, steel, and aluminum, plastic, wood, glass, synthetic material, paper, leather, or another coating layer. The other coating layer may be comprised of the coating composition of the current invention or it may be a different coating composition. The coating compositions of the current invention show particular utility as clearcoats (over base coats, water-borne and solvent-borne), base coats, pigmented topcoats, primers, and fillers. The compositions are particularly suitable for refinishing motor vehicles and transportation vehicles and in finishing large transportation vehicles such as trains, trucks, buses, and airplanes.
The applied coating composition can be cured very effectively at a temperature of, e.g., 0-50xc2x0 C. If so desired, the coating composition may be baked, e.g., at a temperature in the range of 50-120xc2x0 C. The present BOE-functional compound can be prepared in several ways.
One such way is the transesterification of a polyol in an appropriate solvent. Examples of such polyols include glycerol, trimethylol propane, and pentaerythritol. The transesterification agent can be a trialkyl orthoester selected from the group of triethyl orthoformate, triethyl orthoacetate, and triethyl orthopropionate. Preferably, use is made of solvents which are inert to the transesterification reaction, e.g., diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether. The catalyst for such a reaction may be a strong acid, e.g., paratoluene sulphonic acid or BF3Et2O1. Such a process is described in T. Endo et al., Polymer Journal, Vol. 13 (1981), p. 715.
When the polyol selected is pentaerythritol, a BOE group comprising a hydroxyl group is formed. This BOE group is converted into a BOE-functional compound by means of a transesterification reaction or by reaction with an acid chloride. In this way a hydroxyl-functional BOE group can be linked via transesterification to a saturated or unsaturated carboxylic acid, preferably one having not more than 20 carbon atoms. The resulting BOE-functional compound has the advantage of being non-volatile or hardly volatile because of the high molecular weight, while, surprisingly, the viscosity remains low. For this reason the BOE-functional compound is highly suited to be used as a reactive diluent. When the carboxylic acid group is unsaturated, the present coating composition comprising such a BOE-functional compound can be cured in two ways, i.e., via the hydrolyzed BOE group as described above and via the unsaturated compound.
Also, the aforesaid hydroxyl-functional BOE group can be provided with a vinyl group via a transesterification reaction with a (meth)acrylate. By polymerization under the influence of radicals using a vinyl-comprising BOE a BOE-functional polyacrylate can be prepared.
A BOE-functional polyacrylate can further be prepared by the transesterification of a polyacrylate with a hydroxyl-functional BOE group. In this case it is preferred to employ a polyacrylate having short-chain esters, preferably esters having 1-4 carbon atoms. The advantage of such a polyacrylate is that after the transesterification reaction the resulting alcohol groups can be isolated, e.g., by distillation In general, every polymer having an ester group as side group can be provided with BOE groups via said transesterification. As examples of polymers may be mentioned polyesters, polyethers, polyamides, and polyurethanes.
Alternatively, the hydroxyl-functional BOE group can be provided with groups which are reactive or not using, e.g., isocyanate-functional compounds. Furthermore, two or more BOE-functional groups can be interlinked using a di- or polyisocyanate-functional compound. In this way also the hydroxyl-functional BOE group can be linked to, e.g., hydroxyl-functional polymers, e.g., polyester polyols, polyether polyols, and polyacrylate polyols.
Also, BOE-functional compounds can be prepared by converting the corresponding ester-functional oxetane compounds with BF3Et2O1 as described by E. J. Corey et al., Tetrahedron Letters, 24 (1983), pp. 5571-5574.
Oxetane compounds have the following structure: 
wherein R11, R12, R13, R14, and R15 are independently from each other selected from the group of hydrogen and a linear or branched alkyl group having 1-10 carbon atoms; and
R16 is a linear or branched alkyl group having 1-4 carbon atoms substituted with a nucleophilic group selected from the group of hydroxyl, mercaptan, and a primary or secondary amine, and/or with an electrophilic group selected from halogen and derivatives of methane sulphonate, p-toluene sulphonate, and trifluormethane sulphonate.
Preferably, R16 is hydroxymethyl, hydroxyethyl, chloromethyl or chloroethyl. The preparation of oxetane compounds comprising a hydroxyl group is described in J. B. Pattison, J. Am. Chem. Soc., 79 (1957), pp. 3455-3456.
Said hydroxyl-functional oxetane compounds can be converted into ester group-comprising oxetanes via a transesterification reaction with suitable esters R17(COOR18)n, wherein n is an integer of at least 1, R17 is a saturated or unsaturated alkyl, aryl, or acyl radical having 1-40 carbon atoms, optionally substituted with a reactive group such as vinyl, carbonyl, carboxyl ester, or hydroxyl, and R18 is an alkyl group having 1-4 carbon atoms. R18 preferably is methyl, ethyl, or propyl. The alcohols R18OH released on transesterification are isolated from the reaction mixture, e.g., by means of distillation. Such suitable esters may be, for example, the methyl ester of a fatty acid and mixtures of fatty acid, e.g. xe2x80x9cEDENOR(copyright)xe2x80x9d ME C6-10 (available from Henkel Kommanditgesellschaft auf, Dusseldorf, Federal Republic of Germany), and the dimethyl ester of a dimer fatty acid, e.g. xe2x80x9cPRIPOL(copyright)xe2x80x9d 1009, ex. Unichema.
Also, ester group-comprising oxetane compounds can be polymers, with the oxetane compounds being terminal groups or side groups. In that case, R17 can be a polymeric group such as polyester, polyether, polyacrylate, polyamide or polyurethane. Suitable polyesters can be obtained by the nucleophilic addition of carbanions to xcex1,xcex2-unsaturated carbonyl compounds. Likewise suitable are ester group terminated polyesters derived from polycarboxylic acids, polyols, or ester-forming equivalents thereof. Preferably, the aforesaid R18 groups are employed.
Other examples include the adduct of the conversion of diethyl fumarate and diethyl malonate to tetraethyl ester of 1,1,2,3-propane tetracarboxylic acid and a hydroxyl-functional oxetane. In the presence of a diol or polyol a terminal oxetane-functional polyester is formed.
The hydroxyl-functional oxetane compounds also can be converted with the aid of acid chlorides R17(COCl)n.
Preferably, R17 is a group having a high molecular weight, such as pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, or the aforesaid polymers. The resulting BOE compound is non-volatile or hardly volatile because of the high molecular weight, and on account of its surprisingly low viscosity is pre-eminently suited to be used as a reactive diluent.
Halogen-functional oxetanes can be converted into ester-functional oxetanes by reacting them with carboxylate salts of, e.g., silver or with ammonium compounds such as substituted or unsubstituted ammonium salts.
It has now been found that the conversion of the ester-functional oxetane compound in a BOE-functional compound already takes place in the presence of a catalytic amount of a strong Brxc3x8nsted or Lewis acid or organic complexes thereof. Lewis acids are preferred. Examples of Lewis acids are: AlCl3, SbCl5, BF3, BCl3, BeCl2, FeCl3, FeBr3, SnCl4, TiCl4, ZnCl2, and ZrCl4 and organic complexes thereof, e.g., BF3Et2O, BF3-2CH3COOH, BF3-2H2O, BF3xe2x80x94H3PO4, BF3-(CH3)2O, BF3-THF, BF3-2CH3OH, BF3-2C2H5OH, and BF3xe2x80x94C6H5CH2. More preferred are BF3Et2O, BF3-2CH3COOH, and SnCl4. Amounts of 0.001-0.1 mole of catalyst per mole of oxetane compound are preferred, more preferably 0.004-0.08 mole/mole. It has further been found that the conversion already takes place in the presence of a small amount of solvent, and even without solvent if so desired. The term solvent in this connection refers to those solvents which are conventionally employed in the field of organic chemistry and have been described for the conversion of oxetane compounds. The conversion takes place in the range of xe2x88x92100 to 200xc2x0 C., preferably in the range of 0 to 80xc2x0 C. The conversion time is in the range of 30 minutes to 2 days and can result in a yield of more than 90%.
Various methods can be employed to prepare SOE-functional compounds. One such method of preparation is the reaction of an epoxy-functional compound such as butyl glycidyl ether with a lactone such as caprolactone or butyrolactone. Alternatively, SOE-functional polymers can be prepared from epoxy-functional polymers, e.g., polyacrylates of glycidyl(meth)acrylate, using lactones, or from polylactones using monoepoxides. Again, use may be made of catalysts such as Lewis or Brxc3x8nsted acids, preferably paratoluene sulphonic acid or BF3Et2O.
Further, a SOE-functional compound can be prepared by reacting pentaerythritol and triethyl orthopropionate in the presence of paratoluene sulphonic acid with a specific trimethyl benzene being used as solvent. Surprisingly, in this way very selectively a compound having two SOE groups of the following structure 
was synthesized.
The invention will be elucidated further with reference to the following examples.